1. Field of the Invention
This invention relates to hair curling devices which are rapidly heated in microwave ovens and retain heat for a prolonged time. Specifically, the invention deals with gel-filled curler spools containing a gel which can be effectively heated to hair curling temperatures when exposed to microwaves for a very short time and then retain hair curling temperatures for a prolonged time period sufficient to curl hair
2. Description of Related Art
Hair curlers are known for use in drying and curling hair and have been provided in a variety of configurations. Generally, the prior art curlers have comprised molded cylinders or spools of heat transmissive materials such as plastic, which were heated by steam or hot water or which had hollow cores which were fitted around electrically heated rods. Other prior art heated curlers were formed as flexible rod-like bodies which could be bent over themselves to retain a hair tress wound thereon. See, for example, U.S. Pat. No. 4,584,462, issued Apr. 22, 1986, to Morrison. These prior known hair winders or spools required a lengthy pre-heat time before reaching operating temperatures. They also required specialized heating equipment such as steam generators or electrical finger heaters for receiving the spools, and the like.
Microwaveable hair curlers that require no specialized heating equipment are also known. A standard microwave is used to heat an energy retaining material, that is an integral part of the hair curler, to a hair curling temperature. This microwave heating is accomplished more quickly than otherwise.
U.S. Pat. No. 5,988,182 to Engelbrecht discloses microwave heatable rigid cylinders with an annular volume between them containing a granular energy retaining material sealed therein. U.S. Pat. No. 6,079,422 to Drago, see FIGS. 1a-1c, discloses a microwaveable flexible hollow tube, the interior of which contains a granular heat absorbant material 10. FIG. 1a illustrates an end-view of a curler containing a granular heat absorbant material in an annular volume while FIG. 1c illustrates a cross-sectional view of this curler. U.S. Pat. No. 6,064,151 to Gray discloses a microwaveable hair curler consisting of a rigid supporting member for a gel-containing, moisture-emitting and moisture-absorbing sheath, the gel comprising a humectant, water, and a crosslinked water soluble polymer (gel).
Thus, both flexible and rigid forms of microwaveable curlers incorporating a separate heat absorbant material are known. Their energy retaining materials have ranged from cereal grain to moisture-emitting-absorbing gels. However, these devices have been subject to loss or degradation of their energy retaining material through contamination, leakage or wear-out from exposure to microwave energy. In response, prior art curlers have been adapted to enable replacement of their heat absorbing materials.
It would therefore be an improvement in this art to provide microwave heated hair curlers or winders which incorporate long-lived, i.e., effectively permanent, heat absorbant materials.
According to the current invention, there is provided microwave heatable hair winder devices formed from two concentric cylinders with a cellulose, polyacrylic acid, or gum based gel in the annulus between the cylinders and having a hollow core, as illustrated in FIG. 2. The ends of the cylinders are capped to permanently close in, i.e., seal in, the gel. The gel formed from these gel-forming materials and water is highly viscous in the preferred embodiment of the current invention. A biocide also is included in this gel to prevent mold growth and resultant degradation. The gel is heated by microwaving and retains heat for a sufficiently long time such that the invention can be employed as a heated hair curler.
The curlers of the current invention are preferably in the form of hollow molded plastic material spools with cylindrical surfaces around which hair is easily wound. These curlers are made of a heat conductive plastic material that is transparent to microwaves, having a softening point well above hair drying and curling temperature, and which may be comfortably grasped when winding hair around the heated cylindrical portion. A pin 30 is the preferred means for retention of a wound curler, as illustrated in FIG. 3. Prior art retention means have included such pins as well as hair-catching fingers on the outer surface of curlers, as illustrated in FIG. 1b. 
Thus, the curlers of the present invention overcome the disadvantages of the energy retaining materials of the prior art, namely, degradation of these materials with use and elapse of time. Also, because the gel is permanently sealed-in the energy absorbing material will not leak out or ever need to be replaced during the useful lifetime of the curler.